A source with knowledge of the hearing planned for early September told The Hill that Twitter CEO Jack Dorsey and Facebook COO Sheryl Sandberg have both confirmed they will attend the hearing. The source said that Google CEO Sundar Pichai has been invited to testify, as well.

Another source with knowledge of the hearings maintained that formal invitations had not yet been sent to all the companies.

Representatives for Twitter and Facebook both declined to comment on the hearings. Google did not respond to The Hill’s request for comment.

The hearing is a follow-up to the panel's hearing in November, in which lawmakers grilled lawyers from each firm for how their platform was manipulated by Russian trolls seeking to influence the election.